This invention relates to an apparatus and a method for making a battery. More specifically, this invention relates to an apparatus and method for assembling a flexible battery and the resulting flexible battery.
Flexible batteries, which have an enclosure made of a flexible laminate, can be made thin and light in weight, and are capable of conforming to different size and shaped compartments of devices in which they are used. Thus flexible batteries find advantageous use in many consumer electronic devices, such as cellular telephones and camcorders, for example.
Components of a flexible battery, in general, include an anode, a cathode, separator material and electrolyte which are contained within a flexible battery enclosure. The combination of anode, cathode and separator material is known as the electrode assembly. The electrolyte is the medium that serves as the pathway for ionic conduction between the anode and cathode. Liquid electrolyte can include aqueous solutions, for example, sodium hydroxide and potassium hydroxide, or non-aqueous solutions of organic solvents that contain dissolved inorganic salts.
The battery enclosure of a flexible battery is typically made of one or more flexible sheets joined together to produce a laminate. One type of laminate, for example, comprises a metallic foil layer that prevents electrolyte vapor from escaping the battery and also prevents the ingress of external gases. The laminate may also comprise an outer polymer layer that protects the integrity of the metallic foil, and an inner polymer layer that provides a sealing surface for joining the sheets together. Adhesives or tie layers, which bond the individual layers to one another, may also be present.
A flexible battery can be made by placing an electrode assembly between the multi-layered laminates that make up the battery enclosure, and then joining the laminates about the perimeter of the battery enclosure. A portion of the perimeter sealing surfaces is left open so that liquid electrolyte can be dispensed into the battery enclosure and around the electrode assembly. After the electrolyte is added, the opening is sealed.
A sealed battery assembly may incorporate one or more distinct pouches. Where the sealed battery assembly has two pouches, for example, one pouch, the electrode pouch, secures the electrode assembly and a second pouch, the gas pouch, serves as a reservoir for collecting any gas that may be formed or generated by the electrode assembly. Gas may be generated by the electrode assembly during aging, storage, pre-discharge, formation cycling, shipping, handling or combinations thereof. A connecting channel in the battery enclosure connects the two pouches and permits the free flow of gases between them. The opening between the electrode pouch and the gas pouch of the sealed battery assembly can be sealed and the gas pouch can be cut away and discarded, thereby producing a flexible battery.
A problem with flexible batteries, however, is that the sealed surfaces of the battery enclosure can leak. This is due in part to the presence of electrolyte on the sealing surfaces prior to sealing the battery enclosure.
It is desired, therefore, to provide an apparatus and method that minimizes the potential for electrolyte to contact the sealing surfaces of the battery enclosure. It is desired to provide an apparatus and method for producing a flexible battery that is hermetically sealed and fluid-tight.
The present invention is based on recognition and discovery that the problem of electrolyte leakage in a flexible battery can be due in part to the contamination of sealed surfaces by electrolyte prior to sealing the battery enclosure during assembly. The invention, therefore, provides for an apparatus and method for making flexible batteries which reduces or eliminates electrolyte contact on these sealed surfaces when electrolyte is introduced into the battery enclosure.
The present invention provides an apparatus for assembling an electrolyte-tight pouch battery which comprises a support body adapted to support a flexible battery enclosure having an electrode pouch such that the fill opening is located in an upper portion of the electrode pouch for receiving electrolyte. The apparatus also comprises a dispensing element having a discharge orifice that directs the flow of electrolyte inside the electrode pouch when the dispensing element is in the fill position. The discharge orifice directs the flow of electrolyte away from the open portions of the battery enclosure that are subsequently sealed. The fill opening is located in an upper portion of the electrode pouch that is above a predetermined free electrolyte fill level for electrolyte that may accumulate inside the electrode pouch during the filing process.
In one embodiment of the invention, the electrode pouch is oriented prior to filling such that its walls are positioned vertically, or nearly vertically. In this manner gravity aids the filling process and directs the electrolyte away from the sealing surfaces that will be joined together after filling.
In another aspect of the invention, the support body of the apparatus herein supports the battery enclosure during filling in a manner that minimizes the unbounded surface area of electrolyte that is collected in the electrode pouch. Minimization of this unbounded surface of electrolyte reduces the potential for electrolyte to splash, spill or otherwise contaminate the sealing surfaces surrounding openings required for electrolyte filling. With this approach, such openings can be reliably and consistently sealed without exhibiting leakage.
In addition, the present invention provides a method for assembling a fluid-tight flexible battery by arranging the electrode pouch of the battery enclosure such that the fill opening of the electrode pouch is oriented in an upper portion of the electrode pouch, and then dispensing electrolyte from a dispensing element into the electrode pouch. The electrolyte is dispensed away from the sealing surfaces of the enclosure that surround the fill opening to avoid contamination. After filling, the fill opening is sealed to produce a leak-tight flexible battery.
In another aspect of the present invention, the anode tab and the cathode tab that extend from the interior of the battery enclosure to the external area of the battery enclosure do not extend through the fill opening. The portion of the battery enclosure surrounding the anode tab and the cathode tab are sealed prior to the introduction of electrolyte into the battery enclosure to further minimize leakage of electrolyte into the battery enclosure.
These and other aspects and advantages of the present invention will be apparent to those skilled in the art from the following description of the preferred embodiments in view of the accompanying drawings.